1. Field of the Invention
The present invention relates to a cutting tool which is most suitable for use, for example, in machining a valve hole in an engine cylinder head.
2. Description of the Related Art
In a valve hole in a cylinder head, the associated valve frequently abuts the peripheral edge (the opening section) of the hole. In view of this, a hard member made of sintered alloy or the like is fitted into the opening section of the hole to impart the requisite durability to it. Accordingly, to machine such a valve hole, a cutting tool is used which is equipped with cutting inserts for working on the edge of the hole as well as a reaming tool, such as a gun reamer, for finishing the hole itself. Further, in many cases, the peripheral edge portion of the valve hole has a tapered surface so as to be in conformity with the configuration of the associated valve head. To form such a tapered surface, it is desirable for the cutting inserts to be mounted in such a way as to be slidable along a dimension oblique to the axis of rotation of the cutting tool.
FIGS. 5 and 6 show an example of a conventional cutting tool used for the machining of such valve holes.
Referring to the drawings, a tool body 1, which has a substantially conical configuration, is attached, for example, to the spindle end of a machine tool (not shown) to be used for machining, through the intermediation of an adaptor 2, and is rotated around an axis 0 of the machine tool. Further, a bush 3 extending along the axis 0 is fitted onto the front end section of the tool body 1. The shank of a reaming tool, such a gun reamer (not shown), is fitted into the bush 3, so that by advancing this reaming tool while rotating the entire tool body 1, the valve hole can be machine-finished. The advancement of the reaming tool is effected by means of a shaft 4 which is coaxially inserted into a slide shaft described below.
Three cutting inserts 5A, 5B and 5C are provided around the front end section of the tool body 1. By means of the cutting inserts 5, the above-mentioned hole edge portion of the valve hole can be machined. FIG. 5 only shows one cutting insert 5A, the other two cutting inserts 5B and 5C being omitted in the drawing.
The two cutting inserts 5B and 5C are directly fastened to the tool body 1, whereas the cutting insert 5A is slidably mounted thereon. The cutting insert 5A is detachably fastened to a slider 7, which is slidably fitted into a T-shaped groove 6, as shown in FIG. 6, which T-shaped groove is formed in the tool body 1, along the generatrix dimension of the tool body's conical shape, i.e., along a dimension oblique to the axis 0.
The tool body 1 and the adaptor 2 have holes 1a and 2a, respectively, which extend along the axis 0. A slide shaft 8 and a coupling member 9 are inserted into the holes 1a and 2a. The coupling member 9 is fitted into the hole 1a through the intermediation of key 9a, whereby the tool body 1 and the coupling member 9 can integrally rotate around the axis 0. Further, by advancing or retracting the slide shaft 8, the coupling member 9 can advance or retract within the hole 1a. The T-shaped groove 6 and the hole 1a of the tool body 1 communicate with each other through a hole 6a provided at the bottom of the T-shaped groove 6. The slider 7 is equipped with a connecting pin 10, which extends through the hole 6a to protrude into the hole 1a. The tip of the connecting pin 10 is fitted into an oblique hole 9b formed in the coupling member 9, whereby the slider 7 and the coupling member 9 are coupled to each other. Thus, by advancing or retracting the slide shaft 8 together with the coupling member 9, the slider 7 slides along the T-shaped groove 6, thereby causing the cutting insert 5A to slide along a dimension oblique to the axis 0.
To form a valve hole by using this cutting tool, constructed as described above, a reaming tool, such as a gun reamer, is attached to the bush 3, and drawn toward the base end of the tool body 1 by drawing back the shaft 4. Then, the tool body 1 is rotated and, at the same time, fed along the axis 0, whereby the opening edge portion of the valve hole is chamfered by the two cutting inserts 5B and 5C. Subsequently, the tool body 1 is first slightly retracted, and then slide shaft 8 and the coupling member 9 are advanced while rotating the tool body 1, whereby the cutting insert 5A is caused to slide together with the connecting pin 10 and the slider 7, thereby forming a tapered surface as mentioned above on the peripheral edge portion of the valve hole. After this, the reaming tool is advanced by advancing the shaft 4 while rotating the tool body 1, thereby finishing the interior (the valve guide hole) of this valve hole.